Don't reuse closed or mismatched MariaDB clients

grabMariaDBClient reused global.MARIADB_CLIENT whenever the requested
config matched global.CONFIG. It never checked that the client was made
from that config or was still open. init() sets global.CONFIG before
creating the client, so a re-init after a close, or a config change, got
back a closed or wrong client.

- Remember the cache key each client was created with, and compare that
- Wrapping close() drops the client from the cache and unsets
  global.MARIADB_CLIENT, so the next grab or ensureInit makes a new one
- resolveClient goes through grabMariaDBClient instead of repeating the
  global.CONFIG comparison
- Remove the queue test's workaround for this

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/functions/grab-mariadb-client.test.ts

@@ -0,0 +1,38 @@
+import { afterEach, expect, test } from "bun:test";
+import grabMariaDBClient from "./grab-mariadb-client";
+import setMariaDBClient from "./set-mariadb-client";
+
+// Clients connect lazily, so none of these open a connection
+const config = { db_name: "bmt_client_cache", ssl_reject_unauthorized: false };
+
+const originalConfig = global.CONFIG;
+
+afterEach(async () => {
+    await global.MARIADB_CLIENT?.close();
+    global.CONFIG = originalConfig;
+});
+
+test("reuses the client for the same config", () => {
+    expect(grabMariaDBClient({ config })).toBe(grabMariaDBClient({ config: { ...config } }));
+});
+
+test("a closed client is dropped from the cache and the global slot", async () => {
+    setMariaDBClient({ config });
+    const first = global.MARIADB_CLIENT!;
+
+    await first.close();
+    expect(global.MARIADB_CLIENT).toBeUndefined();
+
+    const second = grabMariaDBClient({ config });
+    expect(second).toBeDefined();
+    expect(second).not.toBe(first);
+});
+
+test("the global client is not reused for a different config", () => {
+    setMariaDBClient({ config });
+    global.CONFIG = { db_name: "bmt_other" };
+
+    const other = grabMariaDBClient({ config: global.CONFIG });
+    expect(other).not.toBe(global.MARIADB_CLIENT);
+    other?.close();
+});